This invention relates to the treatment of particulate hydrocarbon fuel such as coal and lignite to reduce dust losses during transportation and storage, to improve cold weather handling properties, and to reduce the incidence of spontaneous combustion. More particularly, the invention relates to a novel composition for spray treatment of particulate hydrocarbon fuel.
Various oils and other materials have in the past been applied to particulate hydrocarbon fuel for the purpose of controlling dust losses. U.S. Pat. Nos. 2,005,512; 2,319,942 and 2,383,543 all describe compositions for spraying coal and the like to control dusting. The normal practice is to use a relatively light oil for this purpose. However, the use of light oil leads to problems such as vaporization, run-off and washing out. U.S. Pat. No. 2,005,512 suggests the use of a hot highly viscous oil to overcome these problems. U.S. Pat. Nos. 2,319,942 and 2,383,543 suggest the use of particular solvent extracts as coal spray oil constituents. Each of the compositions suggested in the above-discussed patents is primarily intended to control dust losses during transportation and storage of the fuel particles.
In the handling and storage of lignite, it is desirable to reduce the normal moisture content of the lignite, which typically is from 25 to 40 percent, in order to reduce transportation costs and to improve the heating efficiency of the material. However, when lignite is dried to a moisture content below 10 to 15 percent, there is a tendency for the material to re-absorb moisture. Further, when lignite is dried to that extent, it becomes unstable and very susceptible to spontaneous ignition during storage. U.S. Pat. No. 2,610,115 describes a process for drying raw lignite followed by mixing the material with a mineral hydrocarbon. The mixture of lignite and mineral hydrocarbon is then heated to further reduce the moisture content and to improve its storage characteristics. More recently, U.S. Pat. No. 3,985,517 describes a process for drying and passivating lignite by treatment with a residual hydrocarbon material.
While the prior art approaches described in the above-discussed references have been successful to varying degrees, there has been a continuing need for an improved composition which, when sprayed on particulate hydrocarbon fuel, will reduce dust losses and spontaneous combustion of the fuel without causing problems from vaporization, runoff or wash-off of the treating composition.